Alligator vs Crocodile: How to Tell Them Apart

Key differences at a glance

Alligators and crocodiles are both crocodilians, the group of large, armored reptiles that also includes caimans and gharials. Alligators and caimans form one family (Alligatoridae), and true crocodiles another (Crocodylidae). Their ancestors split more than 66 million years ago, while dinosaurs still roamed the Earth.

There are only two living alligators: the American alligator and the much smaller, critically endangered Chinese alligator of the lower Yangtze region. True crocodiles include more than a dozen species, from the giant saltwater crocodile to the Nile crocodile and the American crocodile. Every rule below has exceptions, so it is best to check several features together.

In behavior the two groups are much alike. Both are ambush predators that wait in the water for prey, both bask to warm up, and in both the temperature of the nest decides whether eggs hatch as males or females. Mothers of both guard their nests and carry the hatchlings to water in their jaws. Nest building is one point of difference: alligators heap up mounds of rotting plants, while some crocodiles, such as the Nile crocodile, bury their eggs in holes dug in sand, although the saltwater crocodile builds a mound like an alligator.

Snout shape: U versus V

Look at the head from above. An alligator’s snout is broad and rounded, like a shovel or the letter U. A crocodile’s snout is usually longer and narrower, tapering to a point like a V.

Snout shape varies within each group. The mugger crocodile of South Asia has a very broad snout, and the saltwater crocodile’s snout is fairly wide, while the gharial, which is neither an alligator nor a true crocodile, has a pencil-thin snout for catching fish. A broad snout is therefore a good clue, not a guarantee.

Teeth: the toothy grin

The jaws give the most reliable field mark. In an alligator, the upper jaw is wider than the lower jaw, so when the mouth closes the lower teeth fit into sockets inside the upper jaw and are mostly hidden. You see a neat row of upper teeth.

In a crocodile, the upper and lower jaws are about the same width, so the teeth interlock along the outside and both rows stay visible. The enlarged fourth tooth of the lower jaw slots into a notch in the upper jaw and sticks up conspicuously on each side of the snout, even when the mouth is shut.

Color and skin

Adult alligators are dark, usually blackish-gray or deep olive. Crocodiles tend to be lighter: olive, tan or grayish-green, often with darker speckles. Mud and lighting can mislead, but in south Florida an animal that looks almost black is very likely an alligator.

The young differ too. Baby alligators are black with bright yellow crossbands, while young crocodiles are paler with dark bands. Up close, a crocodile’s scales across the whole body carry tiny pits, sensory organs that detect pressure and movement in the water. Alligators have these pits only around the jaws, a difference experts use to identify leather products.

Salt water and habitat

Both groups have glands on the tongue that can remove salt from the body, but they only work properly in crocodiles. As a result, alligators live mainly in freshwater marshes, swamps, rivers and lakes and visit brackish water only briefly. Many crocodiles live in estuaries, mangroves and coastal lagoons, and the saltwater crocodile can travel long distances at sea, though plenty of crocodile species also live in rivers and lakes.

Climate matters as well. Alligators tolerate cold better than any other crocodilian; in winter they become sluggish, and in a freezing pond they can keep their nostrils above the ice. American crocodiles are much more sensitive to cold, which helps explain why they stay at the southern tip of Florida.

Where alligators and crocodiles live

Alligators live only in the southeastern United States and eastern China. Their relatives, the caimans, live in Central and South America. Crocodiles are found across the tropics of Africa, Asia, Australia and the Americas, including many Caribbean islands.

South Florida is the only place in the world where alligators and crocodiles naturally live side by side. Florida’s American crocodiles are found mainly in Everglades National Park, Biscayne Bay, the Florida Keys and the cooling canals of the Turkey Point power plant. Their numbers fell to a few hundred in the 1970s, then recovered to an estimated 2,000 or so, and in 2007 the U.S. Fish and Wildlife Service moved them from endangered to threatened. A few escaped Nile crocodiles have also been caught in south Florida, but there is no evidence that they breed there.

Which is bigger?

It depends on which species you compare. An adult male American alligator usually measures 3 to 4.5 m (10 to 15 ft), while a male American crocodile typically reaches 3 to 4 m (10 to 13 ft), so the two are similar, and the alligator is often heavier for its length.

The biggest crocodiles are in another league. Male saltwater and Nile crocodiles commonly reach 3.5 to 5 m (11.5 to 16.5 ft), and the largest saltwater crocodiles exceed 6 m (20 ft) and 1,000 kg (2,200 lb). At the other extreme, the dwarf crocodile rarely tops 1.9 m (6 ft 3 in). For more detail, see how big do crocodiles get. Lifespans are broadly similar; see how long do alligators live.

Which is more dangerous?

As a rule, the most dangerous crocodilians are crocodiles, but only a few species. The Nile crocodile and the saltwater crocodile cause most fatal crocodilian attacks on people worldwide, partly because of their size and partly because they live close to large human populations.

American alligators bite people only occasionally, usually in or at the edge of water, and deaths are rare. American crocodiles are generally shy, and bites in Florida are very rare. With any crocodilian, the safest approach is to keep well back from the water’s edge, never feed them, and keep children and pets away from shorelines. If someone is bitten, call 911 (US) or local emergency services immediately.

Can alligators and crocodiles interbreed?

No. After more than 66 million years of separate evolution, alligators and crocodiles are far too different to produce offspring together. Hybrids do occur between closely related crocodile species, however. Saltwater and Siamese crocodiles have interbred on crocodile farms, and in the wild, Cuban and American crocodiles hybridize in Cuba and on the Yucatán Peninsula, which worries conservationists working to protect the rare Cuban crocodile.